This invention relates to a process for producing a hollow fiber membrane and a dialyzer of hollow fiber membrane type. More specifically, this invention relates to a process for producing a hollow fiber membrane and a dialyzer of hollow fiber membrane type wherein the hollow fiber membrane is highly biocompatible and presents activation of blood components such as leukocytes and blood platelets.
Blood treating devices of the hollow fiber membrane type have been widely used in extracorporeal blood circulation, haemodialysis, blood oxygenation during open heart surgery, plasma separation, and the like for quite some time. Recently, polymeric hollow fiber membranes were widely employed particularly for the purpose of dialysis, gas exchange, blood component separation and the like.
The polymeric hollow fiber membranes, however, are not free from drawbacks. For example, for the case of patients who have been undergoing heamodialysis by frequently experiencing extracorporeal blood circulation using the above-mentioned blood treating devices complications believed to be caused through activation of the leukocytes and/or platelets have been noted, and such complications have become a serious issue for those undergoing the heamodialysis.
In addition, an increasing number of patients who have undergone heamodialysis for a long period have exhibited a decrease in blood antioxidative properties and a high level of lipid peroxide as well as symptoms of arteriosclerotic diseases which are estimated to have been caused by such conditions.
In order to obviate such problems, JP-B-62-41738 suggests use of an artificial organ wherein a vitamin E is coated on the surface of a dialysis membrane for utilizing various physiological actions of the vitamin E including in vivo antioxidative properties, stabilization of biological membranes, inhibition of platelet coagulation, and the like. Fish oils such as eicosapentaenoic acid are also known to inhibit platelet coagulation.
Such prior art artificial organs, however, had been prepared by a quite complicated and costly process since the vitamin E had to be coated onto the membrane after the production of the dialysis membrane or after the assemblage of the artificial organ. In the method wherein an alcoholic solution of the vitamin E is coated onto a membrane having any micropore after the membrane production, vitamin E pregnates into the micropores of the porous hollow fiber membrane. This process, however, suffers from the defect that a large amount of vitamin E is required for the vitamin E coating.
When a hydrophobic modifier such as a fat-soluble vitamin (e.g. vitamin E) or a fish oil is used by adding such hydrophobic modifier in the core solution comprising water and an organic solvent, water content can not be increased in excess of a certain level since the fat soluble hydrophobic modifier is unsoluble or hardly soluble in water and increased water content in the core solution results in the separation of the hydrophobic modifier from the core solution.
If the vitamin E is incorporated in the hollow fiber membrane in the course of its production by adding the vitamin E in the core solution comprising water and an organic solvent, the fat-soluble vitamin E is hardly soluble in water, and increases the water content which results in the separation of the vitamin E. The separation of the vitamin E from the core solution has to be avoided by limiting the water content to a low level. Such limitation of the water content in the core solution adversely affects uniformity of the coating amount in the inner surface of the membrane or the coagulation of the extruded spinning solution. It is therefore quite difficult to spin a hollow fiber membrane with good membrane structure. For example, in the case of producing a polysulfone hollow fiber membrane in a tube-in-tube type spinner by using a spinning solution containing polysulfone as its main polymer and a core solution, the resulting hollow fiber membrane will suffer from improper membrane structure when the core solution has a water content of less than 20% by weight since the the spinning solution extruded from the outer tube would not be sufficiently coagulated by the core solution ejected from the inner tube.